Benefit of flu shot when exposure is unlikely
November 13, 2023 5:05 AM Subscribe
Not too long ago, I read something about why you should get the flu shot even when exposure is unlikely. Maybe it was that it helps develop broader immunity to the other strains that come along over the years? I don't remember where or when I read it, and with a quick google, I see both that claim and its opposite: a risk of blunted effectiveness. What does the best evidence say?
Take a situation where the flu shot is least important for an individual:
- They're in a dark green (i.e., very low prevalence) area according to this chart, updated weekly.
- Their behavioral factors lower their chance for exposure (e.g. no office job, no kids in school, no large indoor gatherings or indoor restaurants, masked in supermarkets, hand-washing when relevant, etc.).
- They don't have risk factors that'd make a flu case particularly problematic if they did get it.
- The strain that's going around that year is said to be mild.
- [Insert any other risk-mitigating factors here...]
- They're not going to get out of the vaccination habit if they skip a year when the above is all true.
In that case, what benefits (or non-obvious drawbacks) of getting the flu shot still persist, and how's the evidence for them? E.g., does it help develop broader immunity for strains that come along over the years? I'm not really looking for general opinions about getting the flu shot in a case like the above -- more what the known benefits (or drawbacks) are, and the evidence for them.
Take a situation where the flu shot is least important for an individual:
- They're in a dark green (i.e., very low prevalence) area according to this chart, updated weekly.
- Their behavioral factors lower their chance for exposure (e.g. no office job, no kids in school, no large indoor gatherings or indoor restaurants, masked in supermarkets, hand-washing when relevant, etc.).
- They don't have risk factors that'd make a flu case particularly problematic if they did get it.
- The strain that's going around that year is said to be mild.
- [Insert any other risk-mitigating factors here...]
- They're not going to get out of the vaccination habit if they skip a year when the above is all true.
In that case, what benefits (or non-obvious drawbacks) of getting the flu shot still persist, and how's the evidence for them? E.g., does it help develop broader immunity for strains that come along over the years? I'm not really looking for general opinions about getting the flu shot in a case like the above -- more what the known benefits (or drawbacks) are, and the evidence for them.
While COVID has trained us to have to go it alone for these kinds of decisions, this is what the CDC (or other applicable authorities for those outside the US) is for--they issue a recommendation that is intended to be socially beneficial. These recommendations are admittedly not one size fits all--certainly some people would be smart to consult their doctor, but for most people, it's take the recommendation and go.
In other words, your question is interesting (I'd like to know if the flu vaccine conferred benefits without exposure in a given year, but honestly, we're probably exposed), but not actually that useful in deciding whether to get a flu shot.
posted by hoyland at 5:31 AM on November 13, 2023 [5 favorites]
In other words, your question is interesting (I'd like to know if the flu vaccine conferred benefits without exposure in a given year, but honestly, we're probably exposed), but not actually that useful in deciding whether to get a flu shot.
posted by hoyland at 5:31 AM on November 13, 2023 [5 favorites]
So, some years the influenza strains are worse than other years. And this is random and not predictable.
In 2019/2020, long before COVID arrived in Australia; Australia had influenza that killed several healthy, fit 30 and 40 year olds who went to the gym regularly and had no preexisting conditions.
It's worth getting the influenza vaccine every year, just so that you don't become one of those statistics in the years that influenza is really bad.
posted by chariot pulled by cassowaries at 5:39 AM on November 13, 2023 [3 favorites]
In 2019/2020, long before COVID arrived in Australia; Australia had influenza that killed several healthy, fit 30 and 40 year olds who went to the gym regularly and had no preexisting conditions.
It's worth getting the influenza vaccine every year, just so that you don't become one of those statistics in the years that influenza is really bad.
posted by chariot pulled by cassowaries at 5:39 AM on November 13, 2023 [3 favorites]
Best answer: Epidemiologist and vaccine developer here. I don't have time right now to dive into a response beyond a tl;dr (i.e. it's hard to pinpoint individual benefits, but it's exceedingly easy to pinpoint broad, population-scale benefits, no matter what vaccine we're talking about with very, very limited exceptions). Some useful terms for your search include nonspecific/off-target/heterologous effects. Note that funding and resources needed to study these nonspecific effects is a tiny drop in the bucket of biomedical research, so strong evidence (in the form of RCTs looking for these effects, whether positive or negative) is quite limited. There's a lot of data from studies/sources less rigorous than purpose-built RCTs, though.
posted by late afternoon dreaming hotel at 5:44 AM on November 13, 2023 [12 favorites]
posted by late afternoon dreaming hotel at 5:44 AM on November 13, 2023 [12 favorites]
Regarding the prevalence chart, keep in mind that it’s retrospective to begin with and the shot takes up to 2 weeks for maximum efficacy. So if the colors start to change rapidly and the individual’s calculation changes, it may be too late (and an uptick/outbreak in a region could make the shot more difficult to get).
posted by staggernation at 6:10 AM on November 13, 2023 [6 favorites]
posted by staggernation at 6:10 AM on November 13, 2023 [6 favorites]
The Sawbones podcast covered this a few years ago and I'd recommend a listen to that episode.
posted by Nibbly Fang at 6:18 AM on November 13, 2023 [1 favorite]
posted by Nibbly Fang at 6:18 AM on November 13, 2023 [1 favorite]
At the personal level, it's a bit like choosing to have car insurance even though you are an exceptionally safe driver who rarely drives at all. You probably won't need it, but you'll be happy to have it if it turns out to be needed. (The difference, of course, is that you'll probably never know the vaccine was useful -- either you just don't get sick, or maybe you get a mild case instead of sever.)
posted by Dip Flash at 6:21 AM on November 13, 2023 [5 favorites]
posted by Dip Flash at 6:21 AM on November 13, 2023 [5 favorites]
Best answer: There is some evidence that flu shots decrease the risk of Alzheimer's, too, which is a good additiional incentive.
posted by carrienation at 6:22 AM on November 13, 2023 [3 favorites]
posted by carrienation at 6:22 AM on November 13, 2023 [3 favorites]
Response by poster: I get why most of the answers are treating this question as an analog of, “Should I get the vaccine even if….?” As hoyland put it, “your question is interesting (I'd like to know if the flu vaccine conferred benefits without exposure…), but not actually that useful in deciding whether to get a flu shot.” But really, it’s the first part of that I’m asking: evidence about conferred benefits without exposure that year.
posted by daisyace at 6:49 AM on November 13, 2023 [1 favorite]
posted by daisyace at 6:49 AM on November 13, 2023 [1 favorite]
There are 3 new strains each year. So this years 'c' strain would give some protection next year when the shot is made up of 'def' strains. So after the third year there is some protection for nine strains. So cumulative over time. Why they can't give all the strains at once? I guess it's not practical to do thousands at a time.
posted by sammyo at 6:56 AM on November 13, 2023 [2 favorites]
posted by sammyo at 6:56 AM on November 13, 2023 [2 favorites]
I’m relatively low-exposure and low-risk (I work from home, my most regular social interactions are grocery shopping, I’m not quite middle aged) and I never got a flu shot. Until a few years ago, when I had the flu two years in a row, both over the Xmas period. There’s no such thing as a ‘mild’ case of influenza, it’s either bad or worse, and let me tell you I was miserable. Every year since I’ve got my shot as soon as they become available (and the pharmacist was very clear, it’s a vaccine for what’s predicted to be the most prevalent strain/s) and it gives me some peace of mind. That’s a factor not to be discounted here.
posted by macdara at 7:05 AM on November 13, 2023 [3 favorites]
posted by macdara at 7:05 AM on November 13, 2023 [3 favorites]
Why they can't give all the strains at once? I guess it's not practical to do thousands at a time.
sammyo, the reason they can't give all the strains at once is because influenza virus evolves rapidly, and they don't know what the strains of greatest concern are until the the WHO Collaborating Centre for Reference and Research on Influenza sits down and sorts through all the data each year - data based from swabbing the noses of patients who are seriously ill with that years worst influenza strain.
posted by chariot pulled by cassowaries at 7:12 AM on November 13, 2023 [2 favorites]
sammyo, the reason they can't give all the strains at once is because influenza virus evolves rapidly, and they don't know what the strains of greatest concern are until the the WHO Collaborating Centre for Reference and Research on Influenza sits down and sorts through all the data each year - data based from swabbing the noses of patients who are seriously ill with that years worst influenza strain.
posted by chariot pulled by cassowaries at 7:12 AM on November 13, 2023 [2 favorites]
(And yes I know that doesn’t answer the question per se, but I would argue that the question of vaccines is never solely evidentiary; among the many factors that go into it, how it makes you feel really does matter.)
posted by macdara at 7:12 AM on November 13, 2023
posted by macdara at 7:12 AM on November 13, 2023
I don't have any study to back this up and I am relying only on common sense for this, so take it with a grain of salt -
You speak of exposure being "Unlikely". I would simply point out that "Unlikely" does not mean the same as "Impossible". Even though you may be living in the greenest of green zones, and you're staying at home all the time, there's always the chance that the Amazon delivery guy who asks you to sign for a package just moved from an orange zone three days ago, or just came back from visiting his grandma in an orange zone for Thanksgiving, or.....and the map you're watching only captures information as reported to the CDC, so the actual levels of infection could be slightly higher because of stubborn people who aren't seeing their doctor and are just toughing things out. And even for the cases they DO report they are using data that's already happened, instead of predicting future patterns.
posted by EmpressCallipygos at 7:17 AM on November 13, 2023
You speak of exposure being "Unlikely". I would simply point out that "Unlikely" does not mean the same as "Impossible". Even though you may be living in the greenest of green zones, and you're staying at home all the time, there's always the chance that the Amazon delivery guy who asks you to sign for a package just moved from an orange zone three days ago, or just came back from visiting his grandma in an orange zone for Thanksgiving, or.....and the map you're watching only captures information as reported to the CDC, so the actual levels of infection could be slightly higher because of stubborn people who aren't seeing their doctor and are just toughing things out. And even for the cases they DO report they are using data that's already happened, instead of predicting future patterns.
posted by EmpressCallipygos at 7:17 AM on November 13, 2023
At some point along the line I heard something that triggered my innate "collect 'em all" response, and ever since I've gone every year to get the shot. What I heard went something like this:
If you (A) get the flu this year you could get sick. Boo! If you survive, though, you get some immunity for whatever strain of flu you caught and future strains that are related to that strain, forevermore. Yay!
If you (B) don't get the flu this year, you won't get sick from the flu. Yay! but if you don't get the flu and don't get the shot, then your immune system will learn nothing about influenza this year. You will not add immunity to any strains of flu to your immune system's collection. Boo!
If you (C) get the flu shot you are less likely to get the flu and miss out on fun and work. Yay! Even if you do get the flu, you are less likely to get a severe case and end up in the hospital or dead. Yay! Finally, and from my hoarder's perspective, the very best part, you collect some immunity for the strains of flu in the vaccine and future strains that are related to those strains, forevermore. Yay!
Only (C) has just Yay!, no Boo!
(The above of course does not account for the potential that you could contract Guillain Barré or some other complication from the flu shot.)
posted by Don Pepino at 7:25 AM on November 13, 2023 [6 favorites]
If you (A) get the flu this year you could get sick. Boo! If you survive, though, you get some immunity for whatever strain of flu you caught and future strains that are related to that strain, forevermore. Yay!
If you (B) don't get the flu this year, you won't get sick from the flu. Yay! but if you don't get the flu and don't get the shot, then your immune system will learn nothing about influenza this year. You will not add immunity to any strains of flu to your immune system's collection. Boo!
If you (C) get the flu shot you are less likely to get the flu and miss out on fun and work. Yay! Even if you do get the flu, you are less likely to get a severe case and end up in the hospital or dead. Yay! Finally, and from my hoarder's perspective, the very best part, you collect some immunity for the strains of flu in the vaccine and future strains that are related to those strains, forevermore. Yay!
Only (C) has just Yay!, no Boo!
(The above of course does not account for the potential that you could contract Guillain Barré or some other complication from the flu shot.)
posted by Don Pepino at 7:25 AM on November 13, 2023 [6 favorites]
Speaking of "collect em all," I once had an epidemiology professor who said that we should get the flu shot every year because vaccines are like Pokémon and it's always good to exercise your immune system. This is still anecdotal and not scientific evidence, though.
This is the kind of question that a medical librarian might help you find your way to answering. Your public university may have a medical reference librarian on staff that you can call or email with this question. State universities serve the public good and librarians generally provide reference services to state residents.
posted by twelve cent archie at 7:54 AM on November 13, 2023 [1 favorite]
This is the kind of question that a medical librarian might help you find your way to answering. Your public university may have a medical reference librarian on staff that you can call or email with this question. State universities serve the public good and librarians generally provide reference services to state residents.
posted by twelve cent archie at 7:54 AM on November 13, 2023 [1 favorite]
Hi,
I think your question is interesting and nobody has answered it. So, let me break down a few costs/benefits for the group.
Surely, there is a cost/benefit with literally everything in life. And people in high-exposure situations have more to gain than others. Working in a school - your chances of being exposed get bigger and bigger.
This person is very low risk. They also don’t get it brought to them from work. The vaccine effectiveness is usually between 20-50%.
So, does $20 (sometimes free with insurance), a sore arm, and being sick for a day, and a 2-3 hour total trip there, waiting, shot, waiting, home make it worth it?
If someone’s chance of exposure is literally 0 (living in a bomb shelter, perhaps) then obviously they would take more harm than good.
But, generally there could confer other benefits for Mr bomb shelter. That’s the question. What other benefits are there besides what’s on the bottle?
My guess is very little.
posted by bbqturtle at 7:56 AM on November 13, 2023
I think your question is interesting and nobody has answered it. So, let me break down a few costs/benefits for the group.
Surely, there is a cost/benefit with literally everything in life. And people in high-exposure situations have more to gain than others. Working in a school - your chances of being exposed get bigger and bigger.
This person is very low risk. They also don’t get it brought to them from work. The vaccine effectiveness is usually between 20-50%.
So, does $20 (sometimes free with insurance), a sore arm, and being sick for a day, and a 2-3 hour total trip there, waiting, shot, waiting, home make it worth it?
If someone’s chance of exposure is literally 0 (living in a bomb shelter, perhaps) then obviously they would take more harm than good.
But, generally there could confer other benefits for Mr bomb shelter. That’s the question. What other benefits are there besides what’s on the bottle?
My guess is very little.
posted by bbqturtle at 7:56 AM on November 13, 2023
I had a swine flu vax during the Carter administration, and there were articles (that I'll never find) that said it might confer some protection when there was another swine flue outbreak in 2010. You do retain some protection from vaccines, though it does get reduced over time, varying by vax.
Getting the flu shot gives you protection. If you get exposed, you fight it off more rapidly, with fewer symptoms. So you are way less likely to spread the virus to others, who may be at greater risk of harm. It's an opportunity tp provide a community benefit.
posted by theora55 at 8:14 AM on November 13, 2023
Getting the flu shot gives you protection. If you get exposed, you fight it off more rapidly, with fewer symptoms. So you are way less likely to spread the virus to others, who may be at greater risk of harm. It's an opportunity tp provide a community benefit.
posted by theora55 at 8:14 AM on November 13, 2023
Response by poster: bbqturtle's hypothetical bomb shelter resident makes me realize that a hypothetical would be a better way to isolate (heh) what I'm asking. Say someone is going to live on Planet H for a year. There is no flu there and there never will be. Then they'll come back and live their regular, earth-bound life again. Are there known reasons for that person to get the flu shot the year that they'll be on Planet H? For example, does evidence show that it'd be a net positive or negative for their future flu resistance?
posted by daisyace at 8:35 AM on November 13, 2023
posted by daisyace at 8:35 AM on November 13, 2023
I don't remember where or when I read it, and with a quick google, I see both that claim and its opposite: a risk of blunted effectiveness.
As one who is reasonably conscientious about keeping my anti-disinformation vaccinations up to date, I would urge you to follow up those claims of blunted effectiveness to find out whether they're coming from Wakefield-addled ideologues. Typical tells include the co-presence of Just Asking Questions articles suggesting that there might be links between vaccines and autism (such links are, Just Answering Questions, utterly nonexistent) and mentions of thimerosal and/or mercury.
The only "blunted effectiveness" I'm aware of is the simple fact that a vaccination I had twelve months ago is not going to be boosting my immunity to the infections it was made to target to the same extent that it would if I'd had the exact same vaccine two weeks ago. But it would be absolutely typical to find the Wakefield contingent citing sources that explain that effect as evidence in support of the totally horseshit claim that my having had that vax twelve months ago has somehow now reduced my immune system's overall competence.
posted by flabdablet at 8:37 AM on November 13, 2023 [4 favorites]
As one who is reasonably conscientious about keeping my anti-disinformation vaccinations up to date, I would urge you to follow up those claims of blunted effectiveness to find out whether they're coming from Wakefield-addled ideologues. Typical tells include the co-presence of Just Asking Questions articles suggesting that there might be links between vaccines and autism (such links are, Just Answering Questions, utterly nonexistent) and mentions of thimerosal and/or mercury.
The only "blunted effectiveness" I'm aware of is the simple fact that a vaccination I had twelve months ago is not going to be boosting my immunity to the infections it was made to target to the same extent that it would if I'd had the exact same vaccine two weeks ago. But it would be absolutely typical to find the Wakefield contingent citing sources that explain that effect as evidence in support of the totally horseshit claim that my having had that vax twelve months ago has somehow now reduced my immune system's overall competence.
posted by flabdablet at 8:37 AM on November 13, 2023 [4 favorites]
Best answer: I think your question is interesting and nobody has answered it.
Well, sammyo and I answered the question immediately below:
does it help develop broader immunity for strains that come along over the years?...
...and the follow-up question,
Say someone is going to live on Planet H for a year. There is no flu there and there never will be. Then they'll come back and live their regular, earth-bound life again. Are there known reasons for that person to get the flu shot the year that they'll be on Planet H? For example, does evidence show that it'd be a net positive or negative for their future flu resistance?
...in the affirmative: vaccinating against a flu strain that the person never encounters in the year following vaccination can confer benefits for later years.
But now the question is, are our answers reliable? Mine is based on something I heard probably a decade or more ago on some NPR show I cannot now cite. Is it accurate or is it in fact true that there is "a risk of blunted effectiveness?" A 2021 A to a Q in the Harvard Health Letter, citing some weentzysamplesize (250 people) study published in The Journal of Infectious Diseases in 2017, says my vaguely remembered advice from NPR is right. This mouse study published in a 2021 issue of Clinical & Translational Immunology also suggests the NPR advice is right. Per OP somebody on Google says it's wrong. Maybe that someone was "Dr. Edward Belongia and some colleagues at Wisconsin’s Marshfield Clinic Research Foundation," cited in this article from 2015 with no mention of the specific study. If it was Belongia et al. in that article, read to the bottom:
"As for changing the frequency with which the flu vaccine is given, it’s far too soon to even contemplate that kind of move, Belongia said.
“The policy of vaccinating every year has been generally successful,” Belongia said. “We wouldn’t want to change that unless we know for sure that we’re changing it to something that’s going to be better. And right now I don’t think we have any good idea what that would be.’’
posted by Don Pepino at 8:44 AM on November 13, 2023 [1 favorite]
Well, sammyo and I answered the question immediately below:
does it help develop broader immunity for strains that come along over the years?...
...and the follow-up question,
Say someone is going to live on Planet H for a year. There is no flu there and there never will be. Then they'll come back and live their regular, earth-bound life again. Are there known reasons for that person to get the flu shot the year that they'll be on Planet H? For example, does evidence show that it'd be a net positive or negative for their future flu resistance?
...in the affirmative: vaccinating against a flu strain that the person never encounters in the year following vaccination can confer benefits for later years.
But now the question is, are our answers reliable? Mine is based on something I heard probably a decade or more ago on some NPR show I cannot now cite. Is it accurate or is it in fact true that there is "a risk of blunted effectiveness?" A 2021 A to a Q in the Harvard Health Letter, citing some weentzysamplesize (250 people) study published in The Journal of Infectious Diseases in 2017, says my vaguely remembered advice from NPR is right. This mouse study published in a 2021 issue of Clinical & Translational Immunology also suggests the NPR advice is right. Per OP somebody on Google says it's wrong. Maybe that someone was "Dr. Edward Belongia and some colleagues at Wisconsin’s Marshfield Clinic Research Foundation," cited in this article from 2015 with no mention of the specific study. If it was Belongia et al. in that article, read to the bottom:
"As for changing the frequency with which the flu vaccine is given, it’s far too soon to even contemplate that kind of move, Belongia said.
“The policy of vaccinating every year has been generally successful,” Belongia said. “We wouldn’t want to change that unless we know for sure that we’re changing it to something that’s going to be better. And right now I don’t think we have any good idea what that would be.’’
posted by Don Pepino at 8:44 AM on November 13, 2023 [1 favorite]
Are there known reasons for that person to get the flu shot the year that they'll be on Planet H?
Yes. Immunity wanes after time. I suppose the person could just wait out Earth flu season on Planet H but just because it's not flu season doesn't mean flu just magically disappears. You can still get flu in July.
So if our person gets the flu shot in 2023 and moves to Planet H in, say, spring of 2024, by the time their year is up in spring of 2025 the immunity they previously had is gone. But if they get the flu shot in the fall/winter of 2024 on Planet H, they'll have antibodies* for when they move back to Earth in spring of 2025.
*let's just assume that perfect conference of antibodies/immunities works for this exercise
posted by cooker girl at 8:51 AM on November 13, 2023
Yes. Immunity wanes after time. I suppose the person could just wait out Earth flu season on Planet H but just because it's not flu season doesn't mean flu just magically disappears. You can still get flu in July.
So if our person gets the flu shot in 2023 and moves to Planet H in, say, spring of 2024, by the time their year is up in spring of 2025 the immunity they previously had is gone. But if they get the flu shot in the fall/winter of 2024 on Planet H, they'll have antibodies* for when they move back to Earth in spring of 2025.
*let's just assume that perfect conference of antibodies/immunities works for this exercise
posted by cooker girl at 8:51 AM on November 13, 2023
Best answer: LADH came in and dropped some subject expertise above, giving good terms to search with. I am a biologist but not that kind, and took a quick look at the scholarly work on this question of non-specific and/or off target effects of flu shots.
At a glance:
Observations support a pattern whereby live vaccines (such as smallpox vaccine, BCG vaccine, measles vaccine and oral polio vaccine (OPV)) increase resistance to vaccine-unrelated infections, mainly pneumonia and sepsis, and therefore reduce overall mortality more than would be expected from preventing the vaccine-targeted infections. (Nature Reviews Immunology, 2020).
The non-specific effects (NSEs) of vaccines have been discussed for their potential long-term beneficial effects beyond direct protection against a specific pathogen. Cold-adapted, live attenuated influenza vaccine (CAIV) induces local innate immune responses that provide a broad range of antiviral immunity. ...
The results suggest that CAIVs [Live attenuated influenza vaccine] provide short-term, non-specific protection against genetically unrelated respiratory pathogens. [RSV] (Front. Microbiol., 31 January 2018).
Following up on that, we have Non-specific benefit of seasonal influenza vaccine on respiratory syncytial virus-hospitalisations in children (Vaccine, 2023), which showed "Receipt of influenza vaccine reduced RSV-hospitalisations ... We estimated a small protective effect that warrants further investigation."
So, that's a general pattern of beneficial non-specific effects of reducing overall mortality in similar vaccines (i.e. not related to the target pathogen, as well as two good examples of recent work showing that flu vaccine gives an immediate resistance to RSV, and likely other unrelated viruses.
Hopefully that gives you an answer on the benefits of flu shots even if you are never exposed to the flu that year.
posted by SaltySalticid at 9:06 AM on November 13, 2023 [9 favorites]
At a glance:
Observations support a pattern whereby live vaccines (such as smallpox vaccine, BCG vaccine, measles vaccine and oral polio vaccine (OPV)) increase resistance to vaccine-unrelated infections, mainly pneumonia and sepsis, and therefore reduce overall mortality more than would be expected from preventing the vaccine-targeted infections. (Nature Reviews Immunology, 2020).
The non-specific effects (NSEs) of vaccines have been discussed for their potential long-term beneficial effects beyond direct protection against a specific pathogen. Cold-adapted, live attenuated influenza vaccine (CAIV) induces local innate immune responses that provide a broad range of antiviral immunity. ...
The results suggest that CAIVs [Live attenuated influenza vaccine] provide short-term, non-specific protection against genetically unrelated respiratory pathogens. [RSV] (Front. Microbiol., 31 January 2018).
Following up on that, we have Non-specific benefit of seasonal influenza vaccine on respiratory syncytial virus-hospitalisations in children (Vaccine, 2023), which showed "Receipt of influenza vaccine reduced RSV-hospitalisations ... We estimated a small protective effect that warrants further investigation."
So, that's a general pattern of beneficial non-specific effects of reducing overall mortality in similar vaccines (i.e. not related to the target pathogen, as well as two good examples of recent work showing that flu vaccine gives an immediate resistance to RSV, and likely other unrelated viruses.
Hopefully that gives you an answer on the benefits of flu shots even if you are never exposed to the flu that year.
posted by SaltySalticid at 9:06 AM on November 13, 2023 [9 favorites]
For example, does evidence show that it'd be a net positive or negative for their future flu resistance?
There's a very simple line of reasoning in support of the idea that it pretty much has to be a net positive:
Every year, any given location in the world will typically see novel strains of flu going around. Typically those novel strains will be from different lineages than last year's, unless last year's circulating strains did particularly well.
A lot of careful modelling and considered evaluation work goes into predicting what this year's predominant strains are likely to be, and the vaccines that end up getting manufactured and distributed reflect that work.
Those predictions are not - cannot be - 100% accurate every year, exactly because they are predictions. So although the vax you get in any given year has a good chance of being protective against what goes around that year, it can't be fully guaranteed to be. The protection is, by its very nature, always going to be to some extent scattershot.
So if you've been keeping up to date with your vaxes year on year, you're going to get some degree of immunity to a whole bunch of flu strains that didn't circulate much in the years in which you were vaccinated against them.
Evolution is not a linear one-way progression toward some kind of goal state. Flu virus evolution isn't driven by any kind of master plan pushing the flu toward finally becoming capable of evading every conceivable vaccine. What does affect the flu's reproductive success is how immune the population is to this year's common strains, and there's nothing stopping a viral lineage from having another crack at tricks that worked for it in previous years.
So there is a chance that the considered-obsolete vax you had three years ago confers some degree of immunity to whatever strains survived this year as this year's vaccines knock the dominant strains right down. Further, there's a chance that even if this year's predictions miss the mark - perhaps even because they miss the mark - you're better off with a large collection of old-variant reference works available in your immune system's bookcase, even if some of them are getting a bit dusty and motheaten. Don Pepino's hoarder perspective and twelve cent archie's Pokemon-citing epidemiology professor are right on the money.
posted by flabdablet at 9:13 AM on November 13, 2023 [2 favorites]
There's a very simple line of reasoning in support of the idea that it pretty much has to be a net positive:
Every year, any given location in the world will typically see novel strains of flu going around. Typically those novel strains will be from different lineages than last year's, unless last year's circulating strains did particularly well.
A lot of careful modelling and considered evaluation work goes into predicting what this year's predominant strains are likely to be, and the vaccines that end up getting manufactured and distributed reflect that work.
Those predictions are not - cannot be - 100% accurate every year, exactly because they are predictions. So although the vax you get in any given year has a good chance of being protective against what goes around that year, it can't be fully guaranteed to be. The protection is, by its very nature, always going to be to some extent scattershot.
So if you've been keeping up to date with your vaxes year on year, you're going to get some degree of immunity to a whole bunch of flu strains that didn't circulate much in the years in which you were vaccinated against them.
Evolution is not a linear one-way progression toward some kind of goal state. Flu virus evolution isn't driven by any kind of master plan pushing the flu toward finally becoming capable of evading every conceivable vaccine. What does affect the flu's reproductive success is how immune the population is to this year's common strains, and there's nothing stopping a viral lineage from having another crack at tricks that worked for it in previous years.
So there is a chance that the considered-obsolete vax you had three years ago confers some degree of immunity to whatever strains survived this year as this year's vaccines knock the dominant strains right down. Further, there's a chance that even if this year's predictions miss the mark - perhaps even because they miss the mark - you're better off with a large collection of old-variant reference works available in your immune system's bookcase, even if some of them are getting a bit dusty and motheaten. Don Pepino's hoarder perspective and twelve cent archie's Pokemon-citing epidemiology professor are right on the money.
posted by flabdablet at 9:13 AM on November 13, 2023 [2 favorites]
But really, it’s the first part of that I’m asking: evidence about conferred benefits without exposure that year
> I once had an epidemiology professor who said that we should get the flu shot every year because vaccines are like Pokémon and it's always good to exercise your immune system.
I don't have any evidence besides anecdote, and late afternoon dreaming hotel's search terms are probably the most relevant answer here. But besides the 'it can confer immunity for much later exposures' angle, here's another direction to look into: with the covid vaccines, some people with pre-existing chronic conditions like cfs, that are still very poorly understood but are considered to be autoimmune conditions, saw temporary or longer term improvement in symptoms after vaccination for covid. So the 'jogging your immune system' thing might be an interesting direction to look into - although I'm doubtful that there's anywhere near the amount of research on this that there needs to be to give conclusive results.
(As a negative answer to your question, there is always some percentage of people - a very tiny percentage, but still - that have a serious adverse reaction to pretty much any vaccine (or medication or ingested substance in general...) So your Planet H astronaut would still want to weigh the expected hypothetical potential benefit against the expected hypothetical potential risk.)
posted by trig at 9:37 AM on November 13, 2023
> I once had an epidemiology professor who said that we should get the flu shot every year because vaccines are like Pokémon and it's always good to exercise your immune system.
I don't have any evidence besides anecdote, and late afternoon dreaming hotel's search terms are probably the most relevant answer here. But besides the 'it can confer immunity for much later exposures' angle, here's another direction to look into: with the covid vaccines, some people with pre-existing chronic conditions like cfs, that are still very poorly understood but are considered to be autoimmune conditions, saw temporary or longer term improvement in symptoms after vaccination for covid. So the 'jogging your immune system' thing might be an interesting direction to look into - although I'm doubtful that there's anywhere near the amount of research on this that there needs to be to give conclusive results.
(As a negative answer to your question, there is always some percentage of people - a very tiny percentage, but still - that have a serious adverse reaction to pretty much any vaccine (or medication or ingested substance in general...) So your Planet H astronaut would still want to weigh the expected hypothetical potential benefit against the expected hypothetical potential risk.)
posted by trig at 9:37 AM on November 13, 2023
Best answer: You may be interested in this from the CDC: Is it true that getting vaccinated repeatedly can reduce vaccine effectiveness?, which links to a couple studies and is basically answering the same question, framed in a different way.
posted by ssg at 9:56 AM on November 13, 2023 [1 favorite]
posted by ssg at 9:56 AM on November 13, 2023 [1 favorite]
Response by poster: Thanks all, the thread took a kind of circuitous path because I didn't initially frame the question as I should have, but it got there in the end! This is the info I needed -- I appreciate it.
posted by daisyace at 10:09 AM on November 13, 2023 [1 favorite]
posted by daisyace at 10:09 AM on November 13, 2023 [1 favorite]
If low risk of exposure to flu also involves less exposure to other viruses, would there be a benefit just from activating your immune system in some way, so it doesn't atrophy (figuratively speaking)?
posted by demi-octopus at 10:15 AM on November 13, 2023
posted by demi-octopus at 10:15 AM on November 13, 2023
Best answer: 1) Other benefits: The link between influenza and myocardial infarction: vaccination protects.
Impact of Influenza Vaccination on All-Cause Mortality and Hospitalization for Pneumonia in Adults and the Elderly with Diabetes: A Meta-Analysis of Observational Studies.
Several lines of evidence indicate that influenza vaccination may induce nonspecific effects, also referred to as heterologous or pleiotropic effects, that go beyond protection against infection.
Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
2) Some people don't have access to healthcare, so their flus are not recorded. There are reporting lags. The CDC tracker linked in your question relies on data reported to ILINet, the U.S. Outpatient Influenza-like Illness Surveillance Network, consisting of "outpatient healthcare providers in all 50 states, Puerto Rico, the District of Columbia, and the U.S. Virgin Islands." ILINet is a volunteer program, and "elementary, middle, or high school health centers, and any type of institutional setting such as nursing homes and prisons" cannot participate in the program.
In 2021, the Census bureau tallied 54,642 outpatient providers; ILINet receives data from fewer than 3,500.
posted by Iris Gambol at 10:35 AM on November 13, 2023 [1 favorite]
Impact of Influenza Vaccination on All-Cause Mortality and Hospitalization for Pneumonia in Adults and the Elderly with Diabetes: A Meta-Analysis of Observational Studies.
Several lines of evidence indicate that influenza vaccination may induce nonspecific effects, also referred to as heterologous or pleiotropic effects, that go beyond protection against infection.
Flu vaccination has been associated with lower rates of some cardiac events among people with heart disease, especially among those who have had a cardiac event in the past year.
Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COPD) requiring hospitalization).
2) Some people don't have access to healthcare, so their flus are not recorded. There are reporting lags. The CDC tracker linked in your question relies on data reported to ILINet, the U.S. Outpatient Influenza-like Illness Surveillance Network, consisting of "outpatient healthcare providers in all 50 states, Puerto Rico, the District of Columbia, and the U.S. Virgin Islands." ILINet is a volunteer program, and "elementary, middle, or high school health centers, and any type of institutional setting such as nursing homes and prisons" cannot participate in the program.
In 2021, the Census bureau tallied 54,642 outpatient providers; ILINet receives data from fewer than 3,500.
posted by Iris Gambol at 10:35 AM on November 13, 2023 [1 favorite]
VERY anecdotal, but since I've been getting flu shots I haven't had a cold. Make of this what you will.
posted by H21 at 1:59 PM on November 13, 2023
posted by H21 at 1:59 PM on November 13, 2023
This thread is closed to new comments.
(I procrastinated getting my shot, and now I have the actual flu, and let me tell you that I wish I had got the shot. I had fever up to 39C/102F this weekend, and I spent 6 hours coughing my lungs out last night before finally falling asleep at 4am. My back and ribs hurt from the coughing. It may be generally mild, but that's no guarantee it'll develop mild in your body.)
posted by snakeling at 5:18 AM on November 13, 2023 [8 favorites]